A polymer electrolyte fuel cells system wherein a reacted gas that has been passed through a cell stack is enabled to be contacted with an unreacted gas to be passed through the cell stack, thereby carrying out a temperature/humidity exchange for the purpose of preventing the drying of a solid polymer electrolyte membrane. The temperature of the unreacted gas is made lower than the temperature of the reacted gas.
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14. A polymer electrolyte fuel cells system comprising:
a main cell body composed of a cell stack constituted by a laminated body of a plurality of cells each having a solid polymer electrolyte membrane; said main cell body comprising temperature/humidity exchange means which enables a first gas passed through said cell stack to be contacted, through a water retentive-porous body, with a second gas to be passed through said cell stack; and means attached to said porous body, for condensing water vapor contained in the first gas.
5. A polymer electrolyte fuel cells system comprising:
a main cell body composed of a cell stack constituted by a stacked body comprising a plurality of cells each having a pair of gas diffusion electrodes consisting of a fuel electrode and an oxidizing electrode, and a solid polymer electrolyte membrane, said cells being stacked with separators and cooling plates being selectively interposed therebetween, wherein each of said separators includes reactant channels which enable two reactants to take a counter flow with respect to each other; and wherein each of said gas diffusion electrodes has a hydrophilized portion provided at a downstream portion in the flow of the gases.
12. A polymer electrolyte fuel cells system comprising:
a main cell body composed of a cell stack constituted by a stacked body comprising a plurality of cells each having a pair of gas diffusion electrodes consisting of a fuel electrode and an oxidizing electrode, and a solid polymer electrolyte membrane, said cells being stacked with separators and cooling plates being selectively interposed therebetween; each of said separators comprising reactant channels which enable two reactants to take a counter flow in a manner to face each other; and catalyst layers provided at the pair of gas diffusion electrodes excluding downstream portions of the entire passageways of the channels.
1. A polymer electrolyte fuel cells system comprising:
a cell stack constituted by a stacked body of a plurality of cells each having a solid polymer electrolyte membrane; and a temperature/humidity exchanger and a water retentive-porous body, which enables a first gas passed through said cell stack to condense at one surface of the water retentive-porous body, with the condensate thereby produced transferred through the porous body and evaporated at another surface of the water retentive-porous body to contact with a second gas to be passed through said cell stack, and the temperature of said second gas in an inlet of said temperature/humidity exchanger is lower than the temperature of said first gas in the inlet of said temperature/humidity exchanger.
2. The polymer electrolyte fuel cells system according to
3. The polymer electrolyte fuel cells system according to
4. The polymer electrolyte fuel cells system according to
6. The polymer electrolyte fuel cells system according to
wherein each of said cooling plates includes a coolant flow groove, the coolant upstream side of said flow groove being disposed at inlet/outlet portions of the reactant channels in said separator.
7. The polymer electrolyte fuel cells system according to
wherein each of said cooling plates includes coolant flow grooves, and intervals between flow grooves located at inlet/outlet portions of the reactant channels in said separator are made narrower than intervals between the coolant flow grooves that are located other than the inlet/outlet portions of the reactant channels in said separator.
8. The polymer electrolyte fuel cells system according to
reactant channels which enable two reactants to take a counter flow with respect to each other; and cooling means for radiating heat to outer atmosphere, said cooling means being located at inlet/outlet portions of the reactant channels in said separator.
9. The polymer electrolyte fuel cells system according to
10. The polymer electrolyte fuel cells system according to
11. The polymer electrolyte fuel cells system according to
13. The polymer electrolyte fuel cells system according to
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This is a continuation of Application No. PCT/JP99/04817, filed Sep. 6, 1999.
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 10-251124, filed Sep. 4, 1998, the entire contents of which are incorporated herein by reference.
This invention relates to a polymer electrolyte fuel cells system which makes use of a solid polymer as an electrolyte, and in particular to a polymer electrolyte fuel cells system having a mechanism for preventing the drying of a solid polymer electrolyte membrane.
A fuel cells system is designed such that a fuel gas such as hydrogen or a reactive gas is rendered to electrochemically react with an oxidizing gas such as air so as to directly convert the chemical energy of the fuel to an electric energy.
This fuel cells system can be classified into various types depending on the kind of electrolyte. As one type of fuel cells system, there is known a polymer electrolyte fuel cells system which makes use of a solid polymer as an electrolyte.
Referring to
This fuel cells system is constituted by a plurality of cells 4 and a gas-impermeable separator 5 provided with grooves for feeding a reactive gas to each of the electrodes of the cells 4.
According to this fuel cells system, a fuel gas such as hydrogen is fed to the anode 1a, while an oxidizing gas such as air is fed to the cathode 1b so as to allow an electrochemical reaction to take place, thereby generating an electromotive force at each cell 4. This electromotive force of each cell 4 is as low as about 1V at most. Therefore, in order to obtain a high output, a cell stack comprising a laminate body of a plurality of cells 4 is put to practical use as a fuel cells system.
Since the electrochemical reaction in this fuel cells system is exothermic reaction, heat is caused to generate. For the purpose of removing this superfluous heat, a cooling plate 7 allowing a cooling medium to pass therethrough is disposed beside every cell laminate body 6 comprising a plurality of cells 4 which are laminated with a separator 5 being interposed between neighboring cells.
Further, if the fuel gas leaks outside the system, not only the utilization of fuel gas is deteriorated, but also there is a danger of explosion by the fuel gas. Therefore, a gas seal is applied, by making use of a sealing material 8, to a space between the solid polymer electrolyte membrane 3 and the gas-impermeable separator 5.
Additionally, at the location of the cathode 1b, water is generated due to an electrode reaction. When this water is condensed at the electrode reaction site, the diffusion of gas is badly affected. Therefore, the water thus produced is required to be discharged together with unreacted gas outside the cell.
On the other hand, as for the material for the solid polymer electrolyte membrane 3, a perfluorosulfonate film which is a fluorinated ion-exchange membrane is known. This solid polymer electrolyte membrane 3 contains an exchange group or hydrogen ion in its molecule and hence, functions as an ion conductive material when it is saturated with water.
However, once this solid polymer electrolyte membrane 3 is dried on the contrary, the ion conductivity thereof is lowered, thus prominently deteriorating the performance of cell. Therefore, there have been taken various measures to prevent the drying of the solid polymer electrolyte membrane 3.
For example, there is known a method wherein a humidifier constructed to allow water and a reactive gas to pass therethrough is disposed on both sides of a steam-permeating film such as the solid polymer electrolyte membrane 3 so as to allow the reactive gas to be wetted before it is fed to the solid polymer electrolyte membrane 3.
In this case, the humidifier is generally formed integral with the cell stack. Further, it is also known that if a reactive gas to be fed to the anode 1a and cathode 1b is allowed to flow to face each other and at the same time, the operation temperature is controlled to not more than 60°C C. so as to increase the relative humidity of the reactive gas, the generation of power can be achieved without necessitating to humidify the reactive gas.
On the other hand, as shown in Japanese Patent Unexamined Publication H6-132038, there has been also proposed a method of humidifying unreactive gas by introducing both reacted gas and unreacted gas into a gas chamber partitioned by means of a steam permeating film.
In this case, since water vapor is caused to generate on the cathode side 1b due to an electrode reaction, the reacted gas is rendered to contain saturated or nearly saturated water vapor.
On the other hand, since the quantity of water vapor contained in the unreacted gas is relatively small, a difference in partial pressure of water vapor is caused to generate between the reacted and unreacted gases, so that this difference in partial pressure of water vapor can be utilized as a driving force for effecting the concentration diffusion of water vapor.
Further, as shown in Japanese Patent Unexamined Publication H8-273687, there is also proposed to use a hollow fiber as a water vapor-permeating film, wherein unreacted gas is fed through the interior of the hollow fiber and the reacted gas is fed through the exterior of the hollow fiber, thereby humidifying the reactive gas.
Since the contact area between the reacted gas and the unreacted gas can be increased due to the employment of this hollow fiber, it becomes possible to provide a compact humidifier having a high humidification efficiency. Moreover, since a hollow fiber is employed, it becomes possible to incorporate the humidifier inside the gas manifold of the cell stack.
However, these conventional polymer electrolyte fuel cells systems as mentioned above are accompanied with various problems that when the reactive gas is to be humidified by means of a humidifier or through a humidity exchange, the resultant system becomes inevitably sophisticated and difficult to make it compact, and also may raise various problems when it is used in a low temperature environment such as an air atmosphere of 0°C C. or less.
In the case of the humidifier having a structure wherein water and reactive gas are allowed to flow along both sides of a water vapor-permeating film, the freezing of water passageway may be caused to generate when an external temperature is lowered, thus possibly inviting the closing of the passageway, the fracturing of the water vapor-permeating film due to the expansion in volume of ice, and the deformation of the separator 5.
On the other hand, if a non-humidifying operation is to be performed without employing a humidifier, it may become difficult to ensure the long term stability of the solid polymer electrolyte membrane 3 and of the cell performance. In addition to this problem, when the fuel cell is operated at a temperature of not more than 60°C C. which is lower than the ordinary operating temperature of 70 to 90°C C. by making use of a fuel gas containing CO as in the case of a reformed gas, the catalyst in the anode 1a is badly affected by this CO, thus resulting in the promotion of anodic polarization and hence, badly deteriorating the cell performance.
In the case of humidifying the reactive gas by respectively introducing reacted gas and unreacted gas into a gas chamber which is partitioned by means of a water vapor-permeating film, the transfer of water is effected only through a difference in partial pressure between these gases. Therefore, it has been impossible to obtain a sufficient degree of humidification because of a very large magnitude of diffusion resistance of water vapor such as the resistance to diffusion due to the concentration gradient of water vapor on the reacted gas side, the resistance to diffusion inside the water vapor-permeating film, and the resistance to diffusion on the unreacted gas side.
Further, there is also a problem as the cell stack and the humidifier are separately disposed that part of water vapor in the reacted gas is caused to condense in a midway of the tubing for introducing a reacted gas discharged from the cell stack into the humidifier, thereby decreasing the partial pressure of water vapor of the reacted gas to be fed to the humidifier, thus further deteriorating the humidifying efficiency.
When a hollow fiber is employed as a water vapor-permeating film on the other hand, since the transfer of water is effected only through a difference in partial pressure between the reacted gas and the unreacted gas, it has been impossible to obtain a sufficient degree of humidification though the contact area between the reacted gas and the unreacted gas can be increased. Further, if water vapor is condensed inside the hollow fiber to generate liquid water, the discharging of liquid water from the hollow fiber by means of a gas pressure would become difficult due to the capillary force, thus increasing the pressure loss of the gas and hence, deteriorating the efficiency of the system as a whole.
Therefore, an object of the present invention is to provide a polymer electrolyte fuel cells system which makes it possible to circulate water generated at an oxidizing electrode within the cell without sacrificing not only the property of cell but also the simplification and compactness of the system, thereby preventing a solid polymer electrolyte membrane from being dried, and which is excellent in performance and in compactness and capable of reliably actuating the cell system within a short time even if the ambient temperature is as low as not more than 0°C C.
With a view to achieve the aforementioned object, this invention provides a polymer electrolyte fuel cells system comprising a main cell body composed of a cell stack constituted by a laminated body of a plurality of cells each having a solid polymer electrolyte membrane, which is featured in that:
the main cell body is provided with temperature/humidity exchange means which enables a reacted gas passed through the cell stack to be contacted, through a water retentive-porous body, with an unreacted gas prior to a passage of the unreacted gas through the cell stack; and that
the temperature of the unreacted gas is controlled lower than the temperature of the reacted gas.
According to this invention as explained above, the unreacted gas of lower temperature is allowed to contact face-to-face with the reacted gas of higher temperature so as to produce the condensation of water vapor contained in the reacted gas in the interior of the water retentive-porous body, thereby allowing water to permeate close to an interface contacting with the unreacted gas due to an osmotic pressure of the interior of the porous body. Accordingly, a difference in partial pressure of water vapor at the interface contacting with the unreacted gas is caused to increase, thus making it possible to greatly decrease the diffusion resistance of water vapor on the occasion when the water vapor inside the reacted gas is transferred, via the porous body, to the unreacted gas through a temperature/humidity exchange.
According to this invention, there is further provided a polymer electrolyte fuel cells system comprising a main cell body composed of a cell stack constituted by a laminated body of a plurality of cells each having a solid polymer electrolyte membrane, the cells being laminated with a separator and a cooling plate being selectively interposed therebetween, which is featured in that:
the separator is provided with gas-feeding means which enables reactive gases from two lines to flow in a manner to face each other; and that
the cooling plate is provided with a coolant flow groove, the coolant upstream side of the flow groove being disposed at a gate portion of the reactive gases of the two lines in the separator.
According to this invention, there is further provided a polymer electrolyte fuel cells system comprising a main cell body composed of a cell stack constituted by a laminated body of a plurality of cells each having a solid polymer electrolyte membrane, the cells being laminated with a separator and a cooling plate being selectively interposed therebetween, which is featured in that:
the separator is provided with gas-feeding means which enables reactive gases from two lines to flow in a manner to face each other; and that
the cooling plate is provided with coolant flow grooves, intervals between which located at a gate portion of the reactive gases of the two lines in the separator are made narrower than intervals between the coolant flow grooves that are located other than the inlet or outlet portion of the reactive gases of the two lines in the separator.
According to this invention, there is further provided a polymer electrolyte fuel cells system comprising a main cell body composed of a cell stack constituted by a laminated body of a plurality of cells each having a solid polymer electrolyte membrane, the cells being laminated with a separator and a cooling plate being selectively interposed therebetween, which is featured in that:
the separator is provided with;
gas-feeding means which enables reactive gases from two lines to flow in a manner to face each other; and with
cooling means for radiating heat to outer atmosphere, the cooling means being located at a gate portion of the reactive gases of the two lines in the separator.
According to this invention as explained above, since the cooling efficiency becomes higher at a downstream portion of reactive gas where the partial pressure of water vapor is made higher due to water generated by the electrode reaction at the oxidizing electrode as well as due to the consumption of reactive gas, the downstream portion of the reactive gas becomes oversaturated with water vapor, thus causing the condensation of water to occur. The water thus condensed at the portion of the fuel electrode or the oxidizing electrode which is located at the downstream portion of the reactive gas is allowed to permeate into and evaporate from the upstream portion of the reactive gas at the oxidizing electrode or fuel electrode (both electrodes facing each other with a solid polymer film being interposed therebetween) where the partial pressure of water vapor is relatively low. As a result, the partial pressure of water vapor at the upstream portion of the reactive gas can be increased.
According to this invention, there is further provided a polymer electrolyte fuel cells system comprising a main cell body composed of a cell stack constituted by a laminated body comprising a plurality of cells each having a pair of gas diffusion electrodes consisting of a fuel electrode and an oxidizing electrode, and a solid polymer electrolyte membrane, the cells being laminated with a separator and a cooling plate being selectively interposed therebetween, which is featured in that:
the separator is provided with gas-feeding means which enables reactive gases from two lines to flow in a manner to face each other; and a downstream portion, in relative to reactive gas flow, of the gas diffusion electrodes is hydrophilized.
Although the gas diffusion layer is generally made hydrophobic for the purpose of preventing the occurrence of a gas diffusion failure due to water originating from a partial condensation of water vapor in the reactive gas, a downstream portion, in relative to reactive gas flow, of the gas diffusion electrodes is hydrophilized according to this invention as explained above so as to trap the condensed water by this downstream portion, in relative to reactive gas flow, of the gas diffusion electrodes without allowing the condensed water to be discharged. Namely, the water thus trapped by this downstream portion, in relative to reactive gas flow, of the fuel electrode or the oxidizing electrode is then allowed to permeate into an upstream portion of the reactive gas where the partial pressure of water vapor is relatively low in the fuel electrode or the oxidizing electrode, which are faced each other with a solid polymer electrolyte membrane being interposed therebetween, the permeated water being subsequently evaporated. As a result, the partial pressure of water vapor at the upstream portion of the reactive gas can be increased.
According to this invention, there is further provided a polymer electrolyte fuel cells system comprising a main cell body composed of a cell stack constituted by a laminated body comprising a plurality of cells each having a pair of gas diffusion electrodes consisting of a fuel electrode and an oxidizing electrode, and a solid polymer electrolyte membrane, the cells being laminated with a separator and a cooling plate being selectively interposed therebetween, which is featured in that:
the separator is provided with gas-feeding means which enables reactive gases from two lines to flow in a manner to face each other; and the entire passageway of reactive gas in the pair of gas diffusion electrodes excluding a downstream portion of the passageways is provided with a catalyst layer.
According to this invention as explained above, since the catalyst is not attached to a downstream portion of reactive gas where the partial pressure of water vapor is made higher due to water generated by the electrode reaction at the oxidizing electrode as well as due to the consumption of reactive gas, there is no possibility of generating a reaction heat originating from the electrode reaction at this downstream portion of reactive gas, thus enabling to maintain a low temperature of this downstream portion of reactive gas. As a result, the reactive gas can be cooled at the portions of electrodes which are located at this downstream portion of reactive gas, and hence, water vapor becomes oversaturated, thus causing the condensation of water. The water thus condensed at the portion of the fuel electrode or the oxidizing electrode which is located at the downstream portion of the reactive gas is allowed to permeate into and evaporate from the upstream portion of the reactive gas at the oxidizing electrode or fuel electrode (both electrodes facing each other with a solid polymer film being interposed therebetween) where the partial pressure of water vapor is relatively low. As a result, the partial pressure of water vapor at the upstream portion of the reactive gas can be increased.
According to this invention, there is further provided a polymer electrolyte fuel cells system comprising a main cell body composed of a cell stack constituted by a laminated body of a plurality of cells each having a solid polymer electrolyte membrane, which is featured in that:
the main cell body is provided with temperature/humidity exchange means which enables a reacted gas passed through the cell stack to be contacted, through a water retentive-porous body, with an unreacted gas to be passed through the cell stack; and with
means for condensing water vapor contained in the reacted gas, the means being attached to the porous body.
According to this invention as explained above, since water contained in the reacted gas can be removed, it is possible to prevent water from being kept remained in the discharge line of the reacted gas. At the same time, if the air inside a vehicle is employed as air of low temperature, the air can be utilized for heating the interior of the vehicle during a winter season, thus enhancing the efficiency of the system. Moreover, the condensed water can be utilized for the steam modification of a fuel modifier.
Therefore, it is now possible according to the present invention to circulate water generated at an oxidizing electrode within the cell without sacrificing not only the property of cell but also the simplification and compactness of the system, thereby preventing a solid polymer electrolyte membrane from being dried even if the quantity of water vapor in the reactive gas to be fed is small in a non-humidifying operation. Additionally, it is possible to provide a polymer electrolyte fuel cells system which is excellent in performance and in compactness and capable of reliably actuating the cell system within a short time even if the ambient temperature is as low as not more than 0°C C.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.
Various embodiments of this invention will be explained in details with reference to the drawings as follows.
Referring to
In
As shown in
In this embodiment, this water retentive porous body 14 is formed of a hydrophilized non-woven fabric adhered on the surface thereof with a porous membrane having pore diameter of as small as 1 μm or less. It is possible to employ other kinds of material for this porous body 14 such as a hydrophilized carbon plate, a sintered metal sheet, a fluorinated ion-exchange membrane, a composite film comprising a fluorinated porous film laminated with a fibrous polymer material, etc.
What is required for this porous body 14 is that it is capable of holding water condensed from water vapor included in the reacted gas, that the condensed water is allowed to pass through the porous body 14 by the effect of osmotic pressure and then enabled to evaporate due to a difference in partial pressure of water vapor at the interface facing the unreacted gas side, and that the permeability of gases other than water vapor is minimal.
As shown in
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, when a temperature/humidity exchange is allowed to take place between the reacted gas 100 and the unreacted gas 101 at the temperature/humidity exchange portion 10, the water vapor that has been contained in the reacted gas 100 of high temperature that has passed through the cell stack 9 is caused to condense by the effect of the unreacted gas 101 of low temperature, thereby causing this condensed water to cover the region of the porous body 14 which contacts with the reacted gas 100. The condensed water is then caused, due to the osmotic pressure in the interior of the porous body 14, to further penetrate into the porous body 14 up to the vicinity of an interface which contacts with the unreacted gas 101. Therefore, the diffusion resistance of water vapor can be greatly minimized at the moment when the water vapor in the reacted gas 100 is subjected via the porous body to a temperature/humidity exchange with the unreacted gas 101.
Further, since the temperature/humidity exchange portion 10 is disposed to contact with the cell stack 9, a tubing that has been conventionally employed for introducing the unreacted gas 101 into the humidifier (not shown) can be omitted. As a result, the system can be made compact and at the same time, the condensation of water vapor in the reacted gas due to a heat radiation at the tubing can be prevented, thus making it possible to prevent the quantity of water vapor in the reacted gas 101 which is to be fed to the temperature/humidity exchange portion 10 from being decreased.
It is also possible to provide the temperature/humidity exchange portion 10 with a gas-feeding line so as to cause the reacted gas and the unreacted gas to take a counterflow to each other with the porous body 14 being interposed therebetween, thereby making it possible to make the system further compact.
As shown in
As explained above, according to the polymer electrolyte fuel cells system of this embodiment, the water vapor in the reacted gas is caused to condense inside the water retentive porous body 14. As a result, the humidity exchange efficiency can be improved and at the same time, the fuel cells system can be made more compact.
Additionally, since the reacted gas and the unreacted gas are caused to flow in a counter direction to each other, it is possible to make the system further compact.
Further, since a heat exchange means is disposed close to the temperature/humidity exchange portion 10, the quantity of condensation can be increased and hence, the humidity exchange efficiency can be further improved.
As for the cooling means, it is not limited to that shown in this embodiment, but a cooling passageway for flowing a cooling medium such as an antifreezing fluid may be provided in the vicinity of the porous body 14, thus making it possible to achieve almost the same effect as mentioned above.
Although the conventional system where water is employed for the humidification is accompanied with a problem of the freezing of water, water is not employed for the humidification according to the polymer electrolyte fuel cells system of this embodiment, so that it is possible to obviate the problems such as the freezing of water, and the fracture and deformation of the film due to the freezing thereof. As a result, it is possible to provide a polymer electrolyte fuel cells system which is highly reliable and can be actuated within a short time, since a time for melting of ice is no more needed for starting the system.
Referring to
This cell 4 is sandwiched between a gas-impermeable separator 5 provided with reactive gas grooves 13a and 13b for feeding a reactive gas to each electrode, and a cooling plate 7 provided with a groove 13c for flowing a cooling medium, wherein a sealing material 8 is interposed between the cell 4 and the separator 5 as well as between the cell 4 and the cooling plate 7, thereby forming a laminate body. In this case, a plural number of this laminate body are further laminated one another, and the groove 13c for flowing a cooling medium is arranged in such a manner that the upstream portion of the cooling medium is positioned at the gate portion of each reactive gas.
Further, as shown in
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, since the inlet of the cooling plate 7 is disposed at a downstream portion of reactive gas where the partial pressure of water vapor is made higher due to water generated by the electrode reaction at the cathode 1b as well as due to the consumption of reactive gas, the cooling efficiency on the downstream portion of reactive gas can be enhanced so that the downstream portion of the reactive gas becomes oversaturated with water vapor, thus causing the condensation of water to occur. The water thus condensed at the portion of the anode 1a or the cathode 1b which is located at the downstream portion of the reactive gas is allowed to permeate into and evaporate from the upstream portion of the reactive gas at the anode 1a or the cathode 1b (both electrodes facing each other with a solid polymer electrolyte membrane 3 being interposed therebetween) where the partial pressure of water vapor is relatively low. As a result, the partial pressure of water vapor at the upstream portion of the reactive gas can be increased.
Additionally, since the inlet of the cooling plate 7 is disposed at a downstream portion of reactive gas, the relative humidity can be increased at the downstream portion of the reactive gas or the condensation of water can be generated. Accordingly, it is possible to increase the quantity of water vapor to be transferred from the downstream portion of reactive gas at the anode 1a or the cathode 1b where the partial pressure of water vapor is relatively high into the upstream portion of reactive gas at the anode 1a or the cathode 1b where the partial pressure of water vapor is relatively low.
By the way, it has been confirmed that when a non-humidified reactive gas was supplied according to the system of this embodiment, it was possible to obtain almost the same cell performance as that of conventional cell at the operation temperature of 80°C C. which is higher than the conventional operation temperature by about 25°C C. Moreover, since the operation temperature is higher as compared with that of the conventional cell, it was possible to prevent the decrease of voltage by the effect of CO.
As mentioned above, according to the polymer electrolyte fuel cells system of this embodiment, since the partial pressure of water vapor in the reactive gas to be fed to the cell stack can be increased by the presence of the temperature/humidity exchange portion 10 even if a reactive gas of low relative humidity is fed to the cell stack, it is possible to obtain an excellent cell property without requiring to decrease the cell temperature even in the case of a non-humidifying operation.
As a result, the humidifier can be omitted, thus making it possible to make the system compact and to reduce the manufacturing cost. Furthermore, since the cell system can be operated at a higher temperature than the cell temperature on the occasion of feeding a non-humidifying gas according to the prior art, it is possible to inhibit the decrease of voltage by the effect of CO.
Referring to
This cell 4 is sandwiched between a gas-impermeable separator 5 provided with reactive gas grooves 13a and 13b for feeding a reactive gas to each electrode, and a cooling plate 7 provided with a groove 13c for flowing a cooling medium, wherein a sealing material 8 is interposed between the cell 4 and the separator 5 as well as between the cell 4 and the cooling plate 7, thereby forming a laminate body. In this case, a plural number of this laminate body are further laminated one another, and the groove 13c for flowing a cooling medium is constructed in such a manner that the interval between the grooves is relatively narrowed at the gate portion of each reactive gas.
Further, as shown in
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, almost the same effects and advantages as in the case of the aforementioned second embodiment can be obtained.
Referring to
Further, as shown in
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, almost the same effects and advantages as in the case of the aforementioned third embodiment can be obtained.
In particular, when a cooling water is not employed in the cooling of the cell portion, it becomes possible to realize a system where a cooling water is not employed, thus making it possible to improve the handleability of the system.
Referring to
In this case, the entire portions of the anode 1a and the cathode 1b other than the hydrophilization portions 25 thereof are made hydrophobic for the purpose of preventing the gas diffusion layer from becoming poor in gas diffusion due to the condensed water.
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, since an end portion of gas diffusion electrode which corresponds to the downstream portion of the reactive gas is hydrophilized by a coating of ink comprising carbon powder, the condensed water can be trapped by this hydrophilization portion without being discharged. Namely, the water thus trapped at the downstream portion of reactive gas of the anode 1a or the cathode 1b is allowed to penetrate into the upstream portion of the reactive gas at the anode 1a or the cathode 1b (both electrodes facing each other with a solid polymer electrolyte membrane 3 being interposed therebetween) where the partial pressure of water vapor is relatively low, and then, allowed to evaporate therefrom. As a result, the partial pressure of water vapor at the upstream portion of the reactive gas can be increased.
As mentioned above, according to the polymer electrolyte fuel cells system of this embodiment, since the partial pressure of water vapor in the reactive gas to be fed to the cell stack can be increased by the presence of the temperature/humidity exchange portion 10 even if a reactive gas of low relative humidity is fed to the cell stack, it is possible to obtain an excellent cell property without requiring to decrease the cell temperature even in the case of a non-humidifying operation.
As a result, the humidifier can be omitted, thus making it possible to make the system compact and to reduce the manufacturing cost. Furthermore, since the cell system can be operated at a higher temperature than the cell temperature on the occasion of feeding a non-humidifying gas according to the prior art, it is possible to inhibit the decrease of voltage by the effect of CO.
By the way, it is possible, in this embodiment, to employ an ink where a fine powder of SiC, SiO2, TiO2 or SnO2 is substituted for the aforementioned carbon powder, or to employ a solid polymer electrolyte to thereby achieve almost the same effects as mentioned above.
Referring to
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, since the press-fitted portion of the solid polymer electrolyte membrane 3, i.e. the end portion of the gas diffusion electrode which corresponds to the downstream portion of the reactive gas is hydrophilized, the condensed water can be trapped by this hydrophilization portion without being discharged. Namely, the water thus trapped at the downstream portion of reactive gas of the anode 1a or the cathode 1b is allowed to penetrate into the upstream portion of the reactive gas at the anode 1a or the cathode 1b (both electrodes facing each other with a solid polymer electrolyte membrane 3 being interposed therebetween) where the partial pressure of water vapor is relatively low, and then, allowed to evaporate therefrom. As a result, the partial pressure of water vapor at the upstream portion of the reactive gas can be increased.
As mentioned above, according to the polymer electrolyte fuel cells system of this embodiment, since the partial pressure of water vapor in the reactive gas to be fed to the cell stack can be increased by the presence of the temperature/humidity exchange portion 10 even if a reactive gas of low relative humidity is fed to the cell stack, it is possible to obtain an excellent cell property without requiring to decrease the cell temperature even in the case of a non-humidifying operation.
As a result, the humidifier can be omitted, thus making it possible to make the system compact and to reduce the manufacturing cost. Furthermore, since the cell system can be operated at a higher temperature than the cell temperature on the occasion of feeding a non-humidifying gas according to the prior art, it is possible to inhibit the decrease of voltage by the effect of CO.
Referring to
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, since the portion corresponding to the downstream portion of the reactive gas where the catalyst layer 2a or 2b is not attached is incapable of generating a reaction heat by the electrode reaction, the temperature of this portion is lower than that of the electrode reaction portion, thereby increasing the relative humidity or the effect of condensing water at this downstream portion of the reactive gas. As a result, the water vapor on the reacted gas side at the downstream portion of the anode 1a or the cathode 1b is caused to condense, and the water thus condensed at the downstream portion of reactive gas of the anode 1a or the cathode 1b is allowed to penetrate into the unreacted gas side of the anode 1a or the cathode 1b (both electrodes facing each other with a solid polymer electrolyte membrane 3 being interposed therebetween). As a result, the water vapor is allowed to diffuse into the unreacted gas side due to a difference in partial pressure of water vapor, thus performing the humidification of the unreacted gas.
Accordingly, it is possible to increase the quantity of water vapor to be transferred from the downstream portion of reactive gas at the anode 1a or the cathode 1b where the partial pressure of water vapor is relatively high into the upstream portion of reactive gas at the anode 1a or the cathode 1b where the partial pressure of water vapor is relatively low.
By the way, it has been confirmed that when a non-humidified reactive gas was supplied according to the system of this embodiment, it was possible to obtain almost the same cell performance as that of conventional cell at the operation temperature of 85°C C. which is higher than the conventional operation temperature by about 30°C C. Moreover, since the operation temperature is higher as compared with that of the conventional cell, it was possible to prevent the decrease of voltage by the effect of CO.
A Modified Embodiment
As shown in
As mentioned above, according to the polymer electrolyte fuel cells system of this embodiment, since the partial pressure of water vapor in the reactive gas to be fed to the cell stack can be increased by the presence of the temperature/humidity exchange portion 10 even if a reactive gas of low relative humidity is fed to the cell stack, it is possible to obtain an excellent cell property without requiring to decrease the cell temperature even in the case of a non-humidifying operation.
As a result, the humidifier can be omitted, thus making it possible to make the system compact and to reduce the manufacturing cost. Furthermore, since the cell system can be operated at a higher temperature than the cell temperature on the occasion of feeding a non-humidifying gas according to the prior art, it is possible to inhibit the decrease of voltage by the effect of CO.
Referring to
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, if the diffusion of gas is poor at the downstream portion of the reactive gas, the supply of proton would be obstructed, thereby giving rise to the generation of erosion.
For example, when a carbon electrode is employed, the erosion would be generated according to the following reaction.
In this connection, according to the structure of this embodiment, the catalyst layer 2a or 2b is not provided at a portion of each of the anode 1a and cathode 1b which is located in the vicinity of the gate of the reactive gas. As a result, the transfer of proton that has been generated at the anode 1a to the cathode 1b can be obstructed, thus making it possible to prevent the generation of erosion.
By the way, even when the power generation using this embodiment was performed under an operating condition which may cause the deterioration of gas diffusion on the occasion of high load operation or low temperature operation, the erosion of electrodes was not recognized at all.
As explained above, since erosion of electrodes can be prevented according to the polymer electrolyte fuel cells system of this embodiment, the reliability of the cell can be enhanced.
As shown in
The polymer electrolyte fuel cells system according to this embodiment is featured in that it is provided with a humidity exchange portion wherein the reacted gas that has passed through the cell stack is caused to contact, through a water retentive porous body, with air of lower temperature than that of the reacted gas, thereby causing the water vapor contained in the reacted gas to condense inside the water retentive porous body so as to perform a humidity exchange.
Specifically, as shown in
Although unreacted gas is employed in this embodiment, it is also possible to employ part of the gas for the heating of a vehicle.
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, since water vapor is caused to be condensed into water in the porous body 35 and the water thus condensed permeates through the porous body 35 to reach the unreacted gas side, the surface of the porous body 35 facing the unreacted gas side is turned into a wet state, thus maximizing the difference in partial pressure of water vapor. As a result, the unreacted gas is humidified. Further, the water failed to be absorbed as steam by the unreacted gas is utilized as a water for the reforming in the reformer 31 that is disposed on a downstream side of the humidifying section.
According to the polymer electrolyte fuel cells system of this embodiment which is constructed as explained above, since the water vapor contained in the reacted gas can be effectively transferred to the unreacted gas, a water-feeding passageway for humidification is no more required to be provided, so that the problem of freezing can be obviated even when the system is employed at a very cold temperature.
Furthermore, since water contained in the reacted gas is removed, the freezing of discharging line of the reacted gas due to a residual water can be prevented, and at the same time, part of unreacted gas can be utilized as an internal air inside a vehicle for the purpose of heating the interior of the vehicle in the winter season, thus making it possible to improve the efficiency of the system.
Additionally, the water thus condensed can be utilized for the steam reforming of the reformer 31, thus dispensing with the employment of a water tank for reforming and hence, making it possible to enable the system to become more compact.
As explained above, according to the polymer electrolyte fuel cells system of this embodiment, since the reacted gas is contacted through a water retentive porous body with the unreacted gas, the water contained in the reacted gas can be effectively transferred to the unreacted gas. As a result, even if an unreacted gas of low relative humidity is fed to the cell stack, the diffusion resistance of the water vapor can be minimized, thus making it possible to transfer as much quantity of water as possible toward the unreacted gas side, thus enabling to sufficiently humidify the unreacted gas. As a result, even if the system is operated using an unreacted gas of non-humidified state, the power generation can be ensured without lowering the cell temperature.
As explained above, since a humidifier employing water is no more required to be used, the problem of freezing can be obviated even if the ambient temperature is lowered to 0°C C. or less. Therefore, since a process of melting a frozen water can be dispensed with, a fuel cell can be actuated within a shorter time and in a simple procedure.
Moreover, since the system can be simplified and made more compact, and at the same time, since the system can be operated at a higher temperature as compared with the cell temperature to be employed where a non-humidified gas is fed to the system according to the prior art, the lowering of voltage due to the effect of CO can be inhibited, thus making it possible to obtain a polymer electrolyte fuel cells system which is excellent in performance and compact in size.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
Ueno, Mitsushi, Saito, Kazuo, Ogami, Yasuji, Chizawa, Hiroshi
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